In wireless communication, there are two main types of networks, namely “centralized network” and “distributed network”.
In centralized networks, channel time is controlled by a particular control device, commonly called “master device”. Besides the master device, other devices that rely on the master device for network control are commonly called “slave devices”. There are many forms of this centralized network.
Some centralized networks may have a configuration including only one slave device. This kind of network is sometimes called “point-to-point network,” “master/slave pair,” or “master/slave network.” In other forms of centralized network, there may be two or more slave devices connecting to the master device.
This kind of network where there is one master device and two or more slave devices is sometimes called “star-topology network”. FIG. 1 illustrates a typical centralized network with one master device (101) and three slave devices (102), (103) and (104). A Dotted circle (111) represents the area coverage of the network formed by the master device (101). Lines (122), (123) and (124) represent communication and connection links between the slave devices (102), (103) and (104) with the master device (101), respectively.
In a centralized network, only the master device transmits “poll frames” in a periodic manner. Although “poll frame” is sometimes called “beacon frame”, it is referred to here consistently as “poll frame”. A poll frame is a special frame transmitted by a master device, generally for the following purposes:                Allow other devices to discover the master device;        Provide a means to synchronize timing information with the master device, to other devices; and        Provide a means to announce network-related information, to the master device.        
Slave devices generally do not need to transmit poll frames. Instead, slave devices listen for a poll frame from the master device to keep time synchronization and to determine whether the slave devices are allowed to perform transmission. Slave devices generally transmit only commands, data or acknowledgement frames.
A general timing configuration in a communication channel for a centralized network is shown in FIG. 2. The channel time is usually used for transmission of a poll frame (201) by a master device and for a command frame (210) and a data frame (211) by either the master device or slave devices. An acknowledgement frame may be transmitted as well, if necessary.
Non-Patent Literature 1 discloses an example of a centralized network.
On the other hand, in a distributed network, instead of having a single master device to control channel time access as the case of a centralized network, every device controls channel time access in a distributed manner. There is no “master” and “slave” concept because every device can be regarded as an independent “master” itself. Generally, every device in a distributed network transmits poll frames for the following purposes:                Discover an opponent's device one another;        Provide a means to synchronize timing information with itself, to other devices;        Provide a means to announce network related information, to itself; and        Provide a means to avoid and detect transmission interference in a distributed scheme, to itself.        
FIG. 3 illustrates a network topology of a typical distributed network composed of four devices (301), (302), (303) and (304). The network coverage (range) reachable by each of these devices is shown by dotted circles (311), (312), (313) and (314). Each of lines (321), (322), (323), and (324) shows the communication link between two devices.
A general timing structure in a communication channel for a distributed network is shown in FIG. 4. The channel time is usually used for transmission of poll frames (401), (402), (403) and (404) of all devices and for a command frame (410) and a data frame (411) by any devices. Optionally, an acknowledgement frame may be transmitted as well.
Non-Patent Literature 2 discloses an example of a distributed network.